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[73.185.129.58]) by smtp.gmail.com with ESMTPSA id p9sm3936566ilc.63.2021.06.11.12.05.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 11 Jun 2021 12:05:39 -0700 (PDT) From: Alex Elder To: subashab@codeaurora.org, stranche@codeaurora.org, davem@davemloft.net, kuba@kernel.org Cc: bjorn.andersson@linaro.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH net-next 6/8] net: qualcomm: rmnet: clarify a bit of code Date: Fri, 11 Jun 2021 14:05:27 -0500 Message-Id: <20210611190529.3085813-7-elder@linaro.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20210611190529.3085813-1-elder@linaro.org> References: <20210611190529.3085813-1-elder@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In rmnet_map_ipv6_dl_csum_trailer() there is an especially involved line of code that determines the ones' complement sum of the IPv6 packet header (in host byte order). Simplify that by storing the result of computing just the header checksum in a local variable, then using that in the original assignment. Use the size of the IPv6 header structure as the number of bytes to checksum, rather than computing the offset to the transport header. And use ip_fast_csum() rather than ipa_compute_csum(), knowing that the size of an IPv6 header (40 bytes) is a multiple of 4 bytes greater than 16. Add some comments to match rmnet_map_ipv4_dl_csum_trailer(). Signed-off-by: Alex Elder --- .../ethernet/qualcomm/rmnet/rmnet_map_data.c | 26 ++++++++++++------- 1 file changed, 16 insertions(+), 10 deletions(-) diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c index 40d7e0c615f9c..4f93355e9a93a 100644 --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c @@ -120,27 +120,33 @@ rmnet_map_ipv6_dl_csum_trailer(struct sk_buff *skb, struct rmnet_map_dl_csum_trailer *csum_trailer, struct rmnet_priv *priv) { - __sum16 *csum_field, ip6_payload_csum, pseudo_csum, csum_temp; + struct ipv6hdr *ip6h = (struct ipv6hdr *)skb->data; + void *txporthdr = skb->data + sizeof(*ip6h); + __sum16 *csum_field, pseudo_csum, csum_temp; u16 csum_value, csum_value_final; __be16 ip6_hdr_csum, addend; - struct ipv6hdr *ip6h; - void *txporthdr; + __sum16 ip6_payload_csum; + __be16 ip_header_csum; u32 length; - ip6h = (struct ipv6hdr *)(skb->data); - - txporthdr = skb->data + sizeof(struct ipv6hdr); + /* Checksum offload is only supported for UDP and TCP protocols; + * the packet cannot include any IPv6 extension headers + */ csum_field = rmnet_map_get_csum_field(ip6h->nexthdr, txporthdr); - if (!csum_field) { priv->stats.csum_err_invalid_transport++; return -EPROTONOSUPPORT; } + /* The checksum value in the trailer is computed over the entire + * IP packet, including the IP header and payload. To derive the + * transport checksum from this, we first subract the contribution + * of the IP header from the trailer checksum. We then add the + * checksum computed over the pseudo header. + */ csum_value = ~ntohs(csum_trailer->csum_value); - ip6_hdr_csum = (__force __be16) - ~ntohs((__force __be16)ip_compute_csum(ip6h, - (int)(txporthdr - (void *)(skb->data)))); + ip_header_csum = (__force __be16)ip_fast_csum(ip6h, sizeof(*ip6h) / 4); + ip6_hdr_csum = (__force __be16)~ntohs(ip_header_csum); ip6_payload_csum = csum16_sub((__force __sum16)csum_value, ip6_hdr_csum); -- 2.27.0